Pipe bursting and replacement method

ABSTRACT

Tool for slitting and laterally expanding underground steel gas mains and inserting replacement plastic piping into the spread apart pipeline has a forward end cylindrical portion mounting a single, rearwardly angled blade to make only one line of cut, and a conical pipe spreader portion at its rearward end. The conical spreader portion is eccentrically disposed with respect to the forward end cylindrical portion. A single roller type pipe slitter aligned with the fixed blade may be mounted on a removable extension of the forward end cylindrical portion, to initially groove and weaken the pipe along the intended line of cut. A pneumatically operated impact ram is attached to the rearward end of the tool, as is the leading end of the replacement piping. A wire cable pulls the tool through the underground pipe, thereby grooving, slitting and laterally expanding the pipe. The spacing of the roller slitter in advance of the fixed knife blade is dimensionally related to the length of any coupling or clamp as may be anticipated along the line of cut, and the spacing distance of the fixed knife blade forwardly of the conical spreader portion is related to the cone angle of the latter to increase hoop tension immediately in front of the fixed blade as the cutting proceeds.

This is a division of application Ser. No. 07/524,231, filed May 15,1990 now U.S. Pat. No. 4,983,071.

FIELD OF THE INVENTION

This invention relates to techniques for removal and replacement ofunderground pipelines, such as gas mains, service lines and the like.More particularly, the invention relates to apparatus and methods forbursting open and thereby effectively removing such existing butdeteriorated underground steel pipelines, while concurrently feedingreplacement piping into the pipe tunnel thereby created.

BACKGROUND OF THE INVENTION AND THE PRIOR ART

Although the invention may have other uses such as in the replacement ofunderground steel conduits of different size and having a variety ofuses, the invention was made and will therefore be described inconnection with devising an effective manner of removal of steelgaslines extending under paved roads and streets, particularly 4"diameter natural gas mains, and replacing of the gasline with plasticpiping.

As such underground steel gaslines age, they deteriorate and begin toleak. Apart from inherent safety considerations, the repair and eventualreplacement of such deteriorated lines is expensive and disruptive ofnormal street activity taking place thereabove. Expense can besignificantly reduced by replacing the steel gas main with plastic pipeof the same size but, still, the steel pipe must first be effectivelyremoved. In the past, street excavation and trenching along the lengthof the deteriorated steel piping has been necessary. It is intended bythe present invention to avoid such trenching and extensive excavationwhen removing the old pipe.

A successful alternative to such trenching and excavating has beendevised in connection with the removal of cast iron pipelines, thistechnique being known as "pipe bursting". The underground pipe is brokenapart in situ using a pipe bursting tool pulled or pushed therethrough,the tool also incorporating a spreader which pushes the fragmented piperemains radially outward into the surrounding soil so that the pipe iseffectively, though not actually removed to make way for the replacementpipe. The replacement plastic pipe or, alternatively, a larger diameterplastic pipe liner within which the replacement pipe will be received,is usually attached to the pipe bursting tool so that it is pulled intoplace as the old pipe is removed. For example, see the impact ram boringtools of U.S. Pat. No. 4,505,302 (Streatfield et al) and U.S. Pat. No.4,732,222 (Schmidt) which employ pneumatically actuated, so-called"impact moles" of larger diameter than the cast iron pipe to be brokenand having radially projecting angular blades which initially impact andcut into, and break the pipe as the mole is pulled and hammeredtherethrough. Similar disclosures are found in U.S. Pat. Nos. 4,720,211(Streatfield et al), 4,738,565 (Streatfield et al), and 4,674,914(Wayman et al).

However, these conventional percussive pipe breaker devices, thoughsuccessful in replacing cast iron mains, have thus far not beensuccessfully adapted for similar removal of steel gas mains, especiallythose which have all or some of their pipe sections joined usingconventional, so-called Dresser couplings. The reason is that steel pipehas greater hoop strength than does cast iron, is more ductile, andtherefore does not shatter and fragment as does cast iron. Even thechain of alternately upward and downward projecting pipe cutter wheelsfollowed by a concentric conical spreader for cutting and separating thepipe into two halves as described in U.S. Pat. No. 3,181,302 (Lindsay)will not remove steel pipe in an entirely satisfactory manner,especially where local reinforcement is provided at the pipe joints bythe very formidable Dresser couplings. Other possible techniques areknown, such as downhole motors, sawblades, plasma cutters and lasers.However, in addition to their inabilities to satisfactorily perform thedesired bursting function in steel pipe as aforesaid, all appear to beunduly complicated in construction, or expensive, or require very highpower, or are difficult to operate or maintain. Thus, the task ofcutting longitudinally all the way through such steel pipe would beextremely difficult using currently known hardware and methods.

BRIEF DESCRIPTION OF THE INVENTION

Although it may have other uses, the present invention provides a steelpipeline bursting and plastic liner insertion system for replacing gasmains without the high cost of excavation and disruption of streetactivity, and which avoids the aforementioned difficulties of previoussystems if attempted to be used for such purpose. The apparatus andtooling employed is intended to utilize much existing technology toavoid radical experimentation, but to require less power yet operatemore effectively than other systems of its type. It must also be easy touse by utility workers who will normally replace such pipelines.

A guiding concept of the presently proposed technique is the belief thatthe best way to burst a steel pipeline is to split the pipe on only oneline of cut along its length, and to then expand the pipe by spreadingit apart along the line of cut, pushing the pipe wall laterallyoutwardly into the surrounding soil. Preferably, the line of cut will bemade along the bottom of the length of pipe. The advantages of thisapproach include:

1) The split pipe will remain as a single, arch-shaped piece and willresist soil rebound better than if it were split into more than onepiece;

2) The remaining one-piece, laterally spread apart steel pipe willprovide a low-friction surface along which the replacement plastic linerpipe or gas pipeline can slide, thus permitting longer distances betweenthe excavations for the necessary launching and receiving pits at eitherend of the pipe run; and

3) Slitting the pipe along only one line of cut requires less effort,and consequently less energy than slitting it along multiple lines ofcut, or otherwise bursting the pipe to be removed.

In addition, the apparatus utilized in so slitting the pipe must beeffective to similarly slit through commonly used exterior repair clampsand pipe couplings mounted on the pipe at spaced intervals, as may beencountered along the intended line of cut. Particularly, the method andapparatus must be effective to routinely split apart the somewhatmassive Dresser type couplings as will probably be encountered one ormore times along any given length of steel gasline to be replaced, evenalong those in which the pipe sections are more usually welded together.Further, and recognizing that the conventional cone-shaped spreadermounted on the rearward end of the bursting tool is a viable way tospread apart the split pipe and even the Dresser couplings, an object ofthe invention is to devise a means for overcoming the pitching ornosing-over action of the elongated tool as is found to occur when anelongated bursting tool having a concentrically mounted spreader cone ispassed through longer lengths of pipe, which causes its nose to jamagainst the wall of the pipe and requires increased force to pull thetool on through due to unproductive bending of the pipe wall about atransverse axis.

Further, recognizing that a fixed blade is the least complicated mannerof cutting through an object such as a length of steel pipe, but alsorecognizing that blade shape, blade angle, blade size and itsdisposition will greatly affect the ease with which the object can becut, it is intended by the present invention to provide a fixed bladecutter employing the optimum of these aspects of blade technology, asapplied to the intended purpose, and to consider the use of cooperatingancillary devices and mounting relationships as will enhance bladeaction.

Briefly and generally describing the invention in its preferredembodiment, when a length of underground steel gas main piping is to bereplaced, a so-called "launching" pit for introducing the pipe burstingapparatus is excavated at one end of the pipe length to be removed, anda "receiving" pit is excavated at the other end of the length to beremoved. Since the pipeline probably runs continuously through each ofthese pits, the sectional length of the pipe within each pit is cut outand removed, thereby providing an open, entrance end of the pipe withinthe launching pit, and an open, exit end thereof within the receivingpit.

A conventional, hydraulically operated reciprocating wire rope puller ispositioned adjacent to the receiving pit, and a wire pulling rope is fedtherefrom into the receiving pit and thence into the exit end and allthe way through to the entrance end of the pipe length to be removed.The thus fed free end of the wire rope has a connector thereon which isthen attached to the forward end of the elongated pipe bursting andspreading tool provided by the invention, so that the latter may bepulled into and through the pipeline using pulling force exerted by thewire rope puller at the receiving pit. A conventional, pneumatically orhydraulically operated impact ram or "mole" is attached to the other orrearward end of the tool, as is the leading end of the plastic liner orreplacement pipe which is to be inserted into and fed through the areaof the removed pipe as the bursting tool proceeds therethrough. Pullingforce of from five to twenty tons is applied by the wire rope puller topull the bursting and spreading tool through the pipe length t beremoved. A fixed blade mounted on the body of the tool thereby slits thepipe length along only a single line of cut, and an eccentricallydisposed conically shaped spreader portion at the rearward end of thetool causes an outward spreading apart of the slit pipe as the workproceeds. The cutting action is preferably enhanced by the action of asingle roller type pipe slitter mounted in fixed position on the forwardend of the tool in longitudinal alignment with the fixed blade, whichslits partly through and thereby grooves and weakens the pipe thicknessin advance of the fixed blade cutting action. As one or more Dressercouplings or clamps are encountered at locations along the length ofpipe being removed, the impact mole is actuated to augment the wire ropepulling action, and force the fixed blade therethrough. The impact molemay also be actuated while only the pipe wall is being slit, ifnecessary.

The roller slitter on the bursting tool is preferably spaced asufficient distance in advance of the fixed blade such that the rollerslitter will have performed its function of grooving and therebyweakening all of that portion of the pipe length passing through, andreinforced by the Dresser coupling by the time when the fixed bladefirst encounters the Dresser coupling to cut therethrough. Because itwill require very little power to force the fixed blade through theweakened pipe length beneath the Dresser coupling, virtually all of thepower exerted by the fixed blade, due to its being pulled and rammed,will be utilized in forcing it through the structure of the Dressercoupling itself, thus reducing total peak power requirements for thispurpose.

In addition, the eccentrically disposed conical spreader is spaced adistance behind the fixed knife blade such that, considering its coneangle and the amount of lateral spreading apart which it will therebyinduce in the slit pipe, the spreader will also significantly assist thecutting action of the knife blade by generating increased hoop tensionimmediately in front of the blade cutting edge.

Moreover, the manner in which the eccentricity of the conical spreaderportion of the pipe bursting tool is preferably established with respectto the forwardly extending cylindrical body portion on which the fixedknife blade and roller slitter are mounted, is such as to provide a flator straight longitudinal edge all along the length of the tool which iscircumferentially opposite to the blade and slitter, including thatbeneath the conical spreader itself, which avoids the referred to nosingover or pitching of the tool and consequent transverse bending of thepipe wall as is found to occur when using concentrically arrangedconical spreaders.

The preferred fixed blade is comparatively thin and is disposed at anangle of between twenty degrees (20°) and thirty degrees (30°),preferably twenty-five degrees (25°), from the longitudinal axis in therearward direction of the bursting tool. The included angle of theconical spreader portion of the tool is from ten to twenty degrees (10°to 20°), preferably fifteen degrees (15°). The narrow end of the conefaces forwardly, and one of its conical surface generating side elementsis aligned with, and forms a straight continuation of one of thecylindrical surface generating side elements of the forward end portionof the tool on the side thereof which is circumferentially opposite thaton which the fixed blade and roller slitter are mounted.

These and other objects, features and advantages will be more fullyunderstood from the following detailed description of the invention,when taken with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic and fragmentary sectional side viewillustrating the use of the apparatus and the method of the invention;

FIG. 2 is a fragmentary sectional side view of the pipe bursting tooland other apparatus of the invention as are connected thereto;

FIG. 3 is a top plan view of the apparatus shown in FIG. 2;

FIG. 4 is a view of the forward end of the apparatus as seen from lines4--4 in either of FIGS. 2 or 3;

FIG. 5 is a view, partially in section, of the rearward end of theapparatus as seen from lines 5--5 in either of FIGS. 2 or 3;

FIG. 6 is a perspective view, to an enlarged scale, of a preferred blademember which is mounted on the pipe bursting tool illustrated in FIGS.2-5;

FIG. 7 is a similar perspective view of an alternative blade member asmight be mounted on the pipe bursting tool;

FIG. 8 is an end view in cross-section of a pipe bursting toolincorporating the alternative blade of FIG. 7, and showing its operationin bursting a pipe;

FIG. 9 is an exploded view in perspective, to a similarly enlargedscale, of the rotary pipe slitter which is mounted on the pipe burstingtool illustrated in FIGS. 2-5;

FIG. 10 is a fragmentary perspective view of the apparatus illustratedin FIGS. 2-5, showing its operation in slitting and expanding a lengthof underground pipe; and

FIG. 11 is a transverse sectional view, as seen from lines 11--11 inFIG. 10, showing in detail the operation of the roller pipe slitter onthe pipe bursting tool.

Referring to FIG. 1, a pipe bursting and replacement apparatus inaccordance with a preferred embodiment of the invention is generallyindicated by reference numeral 20 and includes a pipe bursting tool,generally indicated by reference numeral 21, and an impact boring ram 22(sometimes referred to in the trade as an "impact mole") removablyconnected to the rearward end 21a of the tool 21 and drivenpneumatically by the compressed air supply 23 via the pneumatic air line24. A wire rope pulling line 25 is removably connected via a coupling 26to the forward end 21b of the tool 21 for pulling the pipe bursting tool21 through the length of underground pipe 27 which is to be effectively,though not actually removed in situ, in the manner to be described.Typically the length of pipe 27 to be removed will be several hundredfeet long, depending upon factors not relevant to this disclosure.Pulling force on the order of from 5 to 40 tons is exerted on thepulling line 25 by a conventional type of wire rope puller, such as thereciprocating cable puller 28 which, in the preferred embodiment, isactually a modified rod pusher made by Powerram Corp. The puller 28 ishydraulically driven by the hydraulic pump 29 via the hydraulic fluidlines 30. As the wire rope 25 is progressively drawn through the puller28 its emerging portion 25a, which is no longer under tension, is woundon to the drum 31.

An alternative method for pulling the tool 21 through the pipe 27 couldutilize a standard rod pusher such as the aforementioned unit byPowerram Corp., or its equivalent. In this instance the rod pusher wouldbe located co-linearly with the pipe 27 and the wire rope 25 would besupplanted by solid or hollow steel rods which are standard with suchrod pushers. Of course, the reciprocating rod pusher would operate inthe pulling, rather than the pulling mode, utilizing the reversiblefeature found on most such units

In the embodiment of the invention being described the pipe 27 to beremoved is a horizontally extending 4" diameter steel pipeline which isburied beneath the ground level 32, usually under a street or roadway(not shown), which is used as a gas main for supplying natural gas froma public utility to homes, factories or other distribution points. Thewall thickness of such typical 4" steel pipe is 0.237". Either wheninitially laid or during a previous repair, the 20' long or 40' longsteel pipe sections 27a, 27b (only two of which are illustrated) whichmake up its length may have been joined using a conventional, exteriormounted pipe joint or coupling 33 which, in the illustrated embodiment,is a standard Dresser pipe coupling. As is well known, the Dresser typepipe coupling includes a closely fitting sleeve or cylindrical ring 33awhich peripherally surrounds the loosely abutted ends of the pipesection 27a, 27b, with a plain or armored gasket material (not shown)being disposed at each end of the ring 33a and forming seals between thering ends and the respective exterior surfaces of the pipe sections 27a,27 b. The gasket material is compressed and held in place by the pair ofend rings 33b at either end of the coupling 33, these being drawntogether by a plurality of peripherally disposed bolts 33c, all as iswell known. For a typical, nominally 4" diameter steel pipe whose actualoutside diameter is 4.5", the length of the middle ring 33a is typically5" or 7" and its thickness is 0.188". The diameters of the respectiveend rings 33b, which are also made of mild steel, is 83/4", and theirgreatest ring thickness adjacent the gasket material is about 3/8".These Dresser couplings are available in various sizes for use on steelpipe sizes of 2" through 12" diameter, and their lengths and otherdimensions are correspondingly greater or less for larger or smallerpipe. Thus, these exteriorly mounted pipe couplings present formidableobstacles to the intended bursting apart of the entire length of thepipe 27, because the couplings 33 must be similarly split apart by thepipe bursting tool as it moves therethrough.

Similarly, where previous repairs to the pipe 27 have been made, it maybe anticipated that elongated pipe clamps 34, each having been installedfor sealing a pipe leak or for strengthening an otherwise weakenedpoint, may be found at various locations along the pipe length 27. As iswell known, each pipe clamp 34 is formed peripherally around the pipeusing a peripherally extending rubber gasket, a stainless steel bridgestrap, and a stainless steel outer peripherally extending band 34a whoseends are drawn together as a hoop by a plurality of longitudinallydisposed rails and transversely extending bolts 34b. These, too, presentformidable obstacles to the passage of the pipe bursting tool along theentire length of the pipe 27, as is intended.

When a gas main such as the length of steel pipe 27 has deteriorated ingeneral condition over the years to an extent where it must be replaced,it is unnecessary to trench and excavate the ground 32 along its lengthto reach and actually remove all of the pipe length 27 from the groundand replace it. Rather, it is only necessary to split or burst the pipelength 27 apart and expand it radially to press its severed parts intothe surrounding soil so as to create a pipe tunnel of enlarged diameter(not illustrated) into which replacement piping, of the same or largerdiameter as that of the removed piping, may be inserted and connected.In general, such manner of pipe replacement is known as "pipe burstingand insertion".

To remove and replace the length of pipe 27 in this manner requiresexcavation to reach and expose the pipe at each end of the length to bereplaced. Thus, with reference to FIG. 1, a launching pit 32a isexcavated to expose an entrance end 27c of the pipe 27, and a receivingpit 32b is excavated to expose the other, exit end 27d of the pipelength 27 to be replaced. The launching pit is made long enough, sayabout 10' feet long, to accomodate the connected lengths of the burstingtool 21 (about 2' long) and its connected impact ram 22 (about 5' long)which will be pulled into the entrance end 27c of the pipe 27. Thereceiving pit 32b is made as small as is convenient for working todisassemble and remove the bursting tool 21 and impact ram 22 as theyemerge from the exit end 27d of the pipe length 27. Although the wirerope puller 28 might be set within the receiving pit 32b in alignmentwith the pipe 27 to exert direct pull on the wire rope 25, in theillustrated preferred embodiment a metal support frame 40 is erectedwithin the receiving pit 32b, having wire rope pulleys 41, 42 mountedthereon as shown, to guide the wire rope 25 out from the receiving pit32b and into the wire rope puller 28 which is mounted atop the framework40.

Of course, as will be understood, when the launching pit 32a andreceiving pit 32b are formed, an exposed section of the pipe 27 (notshown) as would otherwise extend through each of them must be cut outfrom the pipe 27 and removed, to form the exposed entrance and exit ends27c, 27d of the pipe within the respective pits. Thus, severedcontinuations 27e and 27f of the pipe 27 are illustrated as exposed atthe opposite ends of the respective pits 32a, 32b.

Referring now to FIGS. 2-5, the pipe bursting tool 21 of the inventionis a tool for longitudinally and laterally expanding the length ofunderground pipe 27 which is thus to be effectively removed. The leadingend 77a of the plastic replacement pipe 77 is connected to the rearwardend 21b of the tool so as to be thereby pulled into the split andenlarged pipe 27, so that the pipe 27 will be replaced in situ. The tool21 has a cylindrical portion 45, formed by the fixed cylindrical portion45a and the cylindrical portion 45b. The portion 45b may be integrallyformed with the portion 45a or, preferably, is removably connected, asshown, in tandem alignment with the fixed cylindrical portion 45a. Inthe embodiment shown the connection is made using the end of the portion45a, generally indicated by reference numeral 46.

The diameter of the cylindrical portion 45 is slightly smaller than theinside diameter of the pipe 27 within which it will be received. Forexample, the inside diameter of a typical 4" steel pipe presently beingdescribed is 4.026" and, therefore, the outside diameter of thecylindrical portion 45 would be made about 3.75". In this regard, itshould be noted that a 1/8" thick hardened steel skid plate 47, weldedon to the underside of the tool 21, including a portion 47a along theremovable cylindrical portion 45b, locally increases the effectivediameter of the forwardly projecting cylindrical portion 45, as will beunderstood.

The forward end of the removable cylindrical portion 45b has a threadedend 48 to which the correspondingly threaded wire terminator 26 iscoupled by cylindrical connector 49 for removable attachment of the wirepull rope 25, as shown. The threaded end 48 is preferably sized andthreaded identically to the size and threading of the threaded end 46 sothat, when the cylindrical portion 45b is unscrewed and removed from thethreaded end 46, the wire rope connector 49 may be threadedly connectedto the end 46, for reasons which will be explained.

Extending toward the rearward end 21b of the tool 21 from its welded,conjoining attachment along line 50a to the fixed cylindrical portion45a as seen in FIG. 3 is an eccentrically disposed, conically shapedspreader portion 50 of the tool 21, for laterally spreading apart andthereby expanding the burst pipe 27 as will be described. In thepreferred embodiment being described, the portion 50 has right circulartruncated conical shape, its narrower, truncated apex end 50a conjoiningwith and being welded to, or formed with (if cast or fully machined) therearward end of the fixed cylindrical portion 45a, and its base end 50bbeing attached as by welding, or otherwise formed in conjoining relationwith a short-length cylindrical rearward end portion 51 which extends tothe rearward end 21b of the tool 21. The diameter of the enlargedcylindrical portion 51 in the presently described embodiment for 4" pipeis 61/2". The conically shaped spreader portion 50 has an included coneangle A of from ten degrees (10°) to twenty degrees (20°), preferablyfifteen degrees (15°) as shown in FIG. 2 or FIG. 3. One of its conical,surface-generating side elements 50c (FIG. 2) is longitudinally alignedwith, and forms a rearward extension of a cylindrical surface-generatingside element 45c (also FIG. 2) of the fixed cylindrical portion 45a onone side of the tool 21 as shown, so that that side of the tool, towhich the skid 47 is attached, is continuously straight therealong.Thus, on the opposite of the tool as seen in FIG. 2, the conicalsurface-generating side element of the spreader portion 50 is disposedat an angle with respect to the longitudinally extending cylindricalportion 45, which is equal to the included cone angle A, since the shapeof the conical spreader portion 50 is that of a right circular cone.

In a like manner, one of the cylindrical surface-generating sideelements 51c of portion 51 is also longitudinally aligned with, and alsoforms a rearward extension of the aforementioned cylindricalsurface-generating side element 45c of the portion 45a. The effect ofthis continued longitudinal alignment is that the longitudinal axes offixed cylindrical portions 45a and 51 are parallel to each other butoffset, or eccentric, by a distance equal to one half of the differencebetween the respective diameters of cylindrical portions 45a and 51. Theangular disposition of the axis of right circular conical spreaderportion 50 provides a smooth transition between body portions 45a and51, and provides for the alignment of the three respectivesurface-generating side elements 45c, 50c, and 51c.

It will be appreciated that there are numerous ways in which toconfigure the conical spreader portion 50 in addition to the rightcircular conical shape described for the preferred embodiment of FIGS. 2and 3. It is sufficient that spreader portion 50 form a generallyconical transition between the round crossections of fixed cylindricalportions 45a and 51, and that the axes of cylindrical portions 45a and51 be parallel, and that longitudinal alignment exist alongsurface-generating side elements as described above.

A longitudinally extending blade slot 55 (FIG. 2) is formed on the same,opposite side of the tool 21 for receiving a fixed knife blade member56, which is wedged and held in place by a blade back-up piece 57. Theblade member 56 has a forwardly facing and rearwardly angled cuttingedge 56a for slitting the pipe 27, as will be described. As perhaps bestseen in FIG. 6, the rearward angle of the blade member cutting edge 56awith respect to the side surface of the tool 21 from which it projects(FIG. 2) is the angle B, which is from about twenty degrees (20°) toabout thirty degrees (30°). In the preferred embodiment being described,the angle B is twenty-five degrees (25°). Although the width W (FIG. 6)of the base portion 56b and of the blade slot 55 (FIGS. 2 and 3) is 1/2"in the preferred embodiment, the blade thickness T is comparativelythin, e.g. 1/4" in the preferred embodiment. The blade height H projects2" radially outwardly from its associated side surface on thecylindrical portion 45a of the tool 21, and the preferred included angleI (FIG. 6) of the cutting edge 56a itself is forty degrees (40°).

As seen in FIGS. 2 and 3 the fixed blade cutting edge 56a is spaced adistance forwardly away from the conical spreader portion 50. Thisdistance is somewhat critical in that it will determine whether or not,during the action of the spreader portion 50 on the split pipe as willbe described, the spreader portion will generate or establish increasedhoop tension in the pipe 27 at a location immediately in front of thecutting edge 56a as the latter slits the pipe 27 longitudinally. Suchwill facilitate the cutting action, as will be explained. For thispurpose, it has been found that the distance between the point P on thecutting edge 56a which will initially "bite" or contact the pipe 27 andthe location in longitudinal alignment therewith along the line 50a(FIG. 3) of conjoining between the cylindrical portion 45a and theconical portion 50 should be varied depending upon the cone angle of theeccentric spreader. In the preferred embodiment being described whereinthe cone angle of spreader portion 50 is fifteen degrees (15°) thatdistance will be from about one and one-half times to substantiallytwice the diameter of the pipe 27 to be cut, preferably one and one-halftimes the pipe diameter.

An alternative flat top blade 59 a might be similarly mounted in fixedposition on the tool 21 is illustrated in FIG. 7. Its flat surface 59ahas thickness equal to the full width W of the blade member base 56b,preferably 1/2" as shown, and its blade angle B is the same as that ofthe previously described embodiment, i.e, from about twenty degrees(20°) to about thirty degrees (30°), preferably twenty-five degrees(25°). Although its cutting action as will be described is somewhatdifferent from that of the thinner, sharpened blade 56a of thepreviously described embodiment, the flat top blade 59 has advantages ofstrength, and the fact that it does not dull easily and therefore neednot be replaced or sharpened often. Accordingly, it is relativelyinexpensive.

Referring again to FIGS. 2 and 3, and also to FIG. 9, the removablecylindrical portion 45b of the tool 21 has a rotary type pipe slitter 60mounted therein, between respective bearing blocks 61 which are receivedin the opening 62 formed in the cylindrical portion 45b. The opening 62is appropriately longitudinally slotted, as at 63, to receive theslitter wheel 60, as best seen in FIG. 9. The rotary pipe slitter 60 islongitudinally aligned with the fixed blade cutting edge 56a when theremovable cylindrical portion 45b is secured to the fixed cylindricalportion 45a, as seen in FIG. 3. It projects outwardly from the surfaceof the cylindrical portion a distance substantially equal to, orslightly greater than the wall thickness of the pipe 27 to be cut plusthe clearance distance between the interior of the pipe 27 and thesurface of the cylindrical portion 45b when within the pipe 27. Theslitter 60 is a standard pipe cutting wheel having a diameter of 21/4"and blade thickness of about 1/8". As are the fixed blades 56 or 59, theslitter 60 is made of hardened steel, hardened to Rockwell "C" 57 sothat the material is tough, though not brittle. As is the longitudinallocation of the fixed blade 56a with respect to the conical spreaderportion 50, the location along the length of the cylindrical portion 45bof the slitter 60 is functionally related to the operation of the tool21. That is, the axial center C of the slitter 60 is preferablypositioned forward of the blade cutting edge point P a distance which isat least equal to the longest length of any pipe coupling 33 or pipeclamp 34 (FIG. 1) which the tool 21 may be expected to encounter whenpassing through the length of pipe 27, as will be explained. In general,this distance will be at least equal to one and one-half times thediameter of the pipe 27, and may be greater.

The main body of the pipe bursting tool 21, including its spreaderportion 50 and fixed cylindrical portion 45a are preferably made bycasting A.I.S.I 4140 or 4340 low alloy steel. Alternatively, theseparts, as well as the removable cylindrical portion 45b, may be madeusing machined steel components, welded together and hardening asnecessary.

As illustrated in FIGS. 2 and 4, longitudinally extending so-called"junk slots" 65 are formed within the tool body as shown, extending fromthe forward end 21a rearward at least to a location as seen in FIG. 2corresponding to about one-half of the length of the conical portion 50.These openings permit longitudinal passage through and beyond thetravelling tool 21 of rust, scale and dirt deposits as may haveaccumulated within the deteriorated pipe 27 being cut, as will beunderstood. The junk slot function might alternatively be achieved usingadditional longitudinally extending skids, such as skids 47b and 47c(FIG. 11), or built-up lines of weld along the length of the tool,instead of by grooves as shown. Of course, the circumferential locationsof the junk slots, and the number of junk slots provided on the tool maybe varied appropriately to suit particular anticipated conditions.

At its rearward end 21b the pipe bursting tool 21 has a threadedaperture 70 for removable connection of the threaded nose rod 71 of theimpact ram 22. To provide a more rigid connection between the tool 21and the impact ram 22 the tool 21 is provided at its rearward end 21bwith an additional threaded aperture 72, disposed concentrically withrespect to the threaded aperture 70, for receiving a rigid steel ramsupport pipe 73 at its correspondingly threaded forward end 73a. Theinside diameter of the support pipe 73 closely surrounds the cylindricalbody 22a of the ram 22 to avoid bending of the latter with respect totool 21, especially at the threaded nose portion 71.

In addition, a cylindrical pipe receiving flange 75 is attached to therearward end 21b of the bursting tool 21, as shown in FIGS. 2, 3 and 5,for temporary connection, as by screws 76, of the plastic tubular lineror plastic replacement pipe 77 which the tool 21 will progressivelyinsert into the enlarged pipe tunnel (not shown) which is formed as thetool 21 spreads, and effectively removes the deteriorated undergroundpipe 27.

The operation of the pipe bursting and inserting tool and ancillaryapparatus will now be described particularly with reference to FIGS. 1,10 and 11.

As will be generally understood from FIG. 1, after the launching pit 32aand receiving pit 32b have been excavated and the frame 40 and wire ropepuller 28 are positioned as shown, the wire rope 25 is fed off from thewinding drum 31 through the rope puller 28, around the pulleys 42, 41,and then into the exit end 27d of the pipe 27 to be removed. The wirerope and its free end connector 26 are fed or "fished" in any knownmanner through the pipe 27 to emerge from the entrance opening 27cwithin the launching pit 32a. The connector 26 is then threadedlyconnected to the threaded nose 48 of the tool 21, using the cylindricalthreaded connector 49 (FIG. 2). The impact ram 22 and pipe liner orreplacement piping 77 are attached to the rearward end 21b of the tool21, and pneumatic power from the compressed air supply 23 is connectedto the ram 22.

The hydraulic pump 29 is then activated to operate the wire rope puller28 to exert pulling force on the wire rope 25, whereupon the toolforward end 21a is guided into the pipe 27 at its entrance end 27c.Although the tool 21 may be oriented in any circumferential or "roll"position as, for example, with its cutting blade 56 and slitter 60facing upwardly as seen in FIG. 10, as it enters the pipe 27 the tool 21is preferably oriented as illustrated in FIG. 1, with its eccentricspreader portion 50, cutter 56 and slitter 60 facing downwardly so as toslit the pipe 27 along its lowermost longitudinal element. However, forconvenience of illustration, the operation will be described as it wouldbe conducted with these tool elements facing upwardly as shown in FIG.10. It will be understood, however, that the cutting action of the toolwill be the same regardless of its "roll" orientation.

As the pulling force exerted by the rope puller 28 on the wire rope 25is increased to between 5 and 40 tons, the rotary slitter 60, whichfirst engages the pipe 27 will not likely cut through, but will be foundto squeeze the pipe upwardly along the longitudinal line of cut 80 asseen in FIG. 11, and to form a groove 81 along the interior pipe surfaceelement immediately below the line of cut 80, as also indicated in FIG.11. Backing force for the action of the slitter wheel 60 and the actionof blade 56 is provided by the sliding engagement of the skid 47 and 47awith the opposite interior surface of the pipe 27, as also seen in FIG.11. It will be found that this grooving action of the rotary pipeslitter 60 is continuous along the length of the pipe 27 during theslitting and spreading action of the tool 21.

Those skilled in the art will appreciate that it is possible to replacesliding skid 47 with one or more rolling idler elements or wheels (notshown). These idler wheels would also provide the backing force for theaction of slitter wheel 60 and blade 56, with the added advantage oflower friction but with the disadvantage of increased cost andsusceptability to dirt and foreign matter. Likewise, practice of theinvention has shown that the addition of auxilliary skids such as 47band 47c (FIG. 11) can help maintain the pipe crossection in a circularshape, thereby assisting the action of slitter wheel 60.

It will be understood that the forming of the interior groove 81 thinsthe pipe wall thickness along the line of cut 80 so that the cuttingaction of the knife blade 56a therealong is facilitated, thus requiringless power to pull the knife blade through the pipe 27, and imposingless wear on the fixed blade 56.

Moreover, as will be understood from FIG. 10, the subsequent lateralspreading apart of the slit pipe 27 by the spreader portion 50 of thetool 21 exerts a longitudinal tearing action on the intended line of cutalong the as yet unslit pipe, immediately forward of the blade cuttingedge 56a, thereby significantly increasing hoop tension within the pipe27 at that point, which further facilitates the cutting action. Aspreviously noted, this establishment of hoop tension immediately infront o the fixed cutting blade is determined by the positioning of theblade at a fixed distance forwardly of the tool spreader portion 50,considering the conical shape of the spreader portion. That is, if thefixed knife blade 56 is located too far forwardly, the spreader portion50 will have no effect on the pipe immediately forward of the cuttingblade, and the action of the fixed blade will not benefit from thetension. If the knife blade 56 is positioned too far rearwardly, thehoop tension induced by the spreader portion 50 will tend to beestablished at a location too far forwardly of the knife blade, in whichcase slitting of the pipe occurs only because of the tearing action ofthe spreader portion and not due to any knife blade action at all. Inthe latter case the ability of the tool to split couplings and clamps isseverely compromised or defeated because the tearing action of thespreader portion 50, and hence the forward progress of the entire tool,will likely be halted when the spreading/tearing action encounters thelocal pipe reinforcement represented by a coupling or clamp. The optimumtool proportions and blade locations cited herein permit the fixed blade56 to enter and cut a coupling before the spreading/tearing action (andforward progress) are halted, yet still allow the spreading action andresulting hoop tension to facilitate the cutting action of the fixedblade. It becomes apparent that if the cone angle of the spreader ischanged, the fixed position of the knife blade should also be changed toa location either farther from or nearer to the spreader. If the coneangle of the spreader is made shallower, the knife blade should bepositioned farther in front of the spreader; if the cone angle is madewider, the blade should be moved closer to the spreader. In this regardit will be noted that shallower cone angles impart greater "wedgingaction", and therefore generally induce greater hoop tension in the pipefor a given rope pulling force. As previously mentioned, it is believedthat a spreader cone angle within the range of between ten degrees (10°)and twenty degrees (20°) affords good wedging action, with the preferredangle being fifteen degrees (15°), and that for such shallow cone anglesthe cutting blade should be positioned at a distance of between one andone-half (11/2) and two (2) times the nominal diameter of the pipe 27,forwardly of the truncated apex end 50a of the conical spreader.

Depending upon the soil resistance encountered, supplemental rammingforce of the impact ram 22 may or may not be required. That is, in lessdense and/or less compacted soil, such as sandy soil, the force exertedby the rope puller 28 may be entirely adequate to pull the pipe burstertool 21 in its cutting action through the wall thickness of the pipe 27.In such instances the removable cylindrical portion 45b and the slitter60 mounted thereon, may be removed. On the other hand, in dense, orcompacted, or hard clay soil as well as in instances in which pipecouplings 33 and clamps 34 may be encountered as aforesaid, theaugmenting repeated hammering force of the impact ram 22 may be requiredto slit the pipe wall. In the presently described embodiment wherein 4"diameter steel pipe is being split a typical impact ram 22 would be aPierce Airrow PA-4 pneumatic underground piercing tool which exerts 420blows per minute, each with an impact force of 190 lbs. Other typicalPierce Airrow tools as may be used for up to 6" diameter pipe provide upto 620 blows per minute, with impact forces of from 70 to 190 lbs.Larger rams may be employed for larger pipe sizes.

As noted, the grooving action of the slitter wheel 60 is intended to beperformed considerably in advance of the actual slitting apart of thepipe 27. It becomes apparent that such grooving can be performed in anoperation which is conducted in advance of and separate from the cuttingand bursting action of the fixed blade 56 and conical spreader portion50. Thus, referring again to FIG. 1, such two-stage operation could beconducted by utilizing an unmodified standard rod pusher (not shown)within the receiving pit 32b, in alignment with the pipe exit end 27dand pushing connected lengths of rod through the pipe 27, with only theremovable cylindrical portion 45b (FIG. 2) connected to the leading endof the first length of rod to be introduced into the pipe end 27d. Theslitter wheel 60 thereon would be pushed through by the connected rodsand would groove the pipe 27 from its exit end 27d to its entrance end27c, whereupon the cylindrical portion 45b would be detached therefromwithin the launching pit 32a, and the forward end of the pipe burstingtool cylindrical portion 45a would be attached to the rod end. The rodpusher would then be reversed so as to pull the lengths of rod and thebursting tool back through the pipe 27 to the receiving pit 32b so thatthe pipe is thereby slit and laterally expanded by its fixed knife blade56 and it conical spreader portion 50. In this way the more fragileslitter wheel 60 would not be subjected to the pounding delivered by theimpact ram 22 if its use is necessary during the slitting and burstingoperation. Of course, the same two-stage operation of grooving and thenslitting and bursting the pipe could also be performed using two pullingpasses with the wire rope 25, the first pulling the detached cylindricalportion 45b with its slitter wheel 60 through the pipe, and the secondpass being made with only the fixed cylindrical portion 45a and itsconjoining spreader portion 50 to slit and burst the pipe.

Referring again to FIG. 10, using the preferred cone angle of thespreader portion 50 and the preferred position of the blade member 56 aspreviously described, it will be found that the conical spreader portion50 induces a small longitudinal tear, indicated by reference numeral 82,immediately in front of the contact point P of the blade cutting edge56a, so that the force required to move the blade along the line of cut80, 82 is significantly reduced.

Using the combined pulling action of the wire rope 25 and the hammeringaction of the impact ram 22, it will be found that the tool 21 easilyslits through and spreads apart any pipe coupling 33 or pipe clamp 34(FIG. 1) as may be encountered along the length of the pipe 27. Aspreviously pointed out, the cutting action of the knife blade 56a andthe conical spreader portion 50 through any coupling 33 or pipe clamp 34is augmented by the grooving 81 and consequent weakening of the pipewall thickness along the intended line of cut 80 as the slitter 60passes beneath the end rings 33b and middle ring 33a of the coupling 33in advance of any contact of the knife blade cutting edge 56a with thecoupling or the clamp.

The amount of pulling force required is also significantly reduced bythe fact that the tool 21 is required to cut along only a single line ofcut 80 through the pipe 27, and by the eccentrically arranged spreaderportion 50 whose spreading action is concentrated along that one line ofcut and only the adjacent side wall portions of the pipe.

The eccentric disposition of the conical spreader portion 50 as shownand described, and which provides a completely straight reaction edgealong its opposite side, additionally prevents pitching or nosing-overmovement of the tool 21 as it is pulled and rammed through the pipe 27.

Further, the cutting of the pipe 27 along only one line of cut 80produces an arch-like expanded shape of the slit pipe, as indicated byreference numeral 85 in FIG. 10, which affords a smooth interior surfacealong which the plastic liner or replacement pipe 77 may slide as it isinserted, thereby further reducing required forces. The arch-like form85 of the slit pipe when produced as an inverted U-shape as indicated inFIG. 1, has the additional advantage of shielding the thus produced pipetunnel from rebound or other entry of dirt from the surroundingcompacted soil.

With reference to FIG. 8 it will be noted that, when using the flat topblade 59, the line of cut 80 of the pipe 27 is actually made by only oneof the its longitudinal, angularly disposed edges 59c or 59d. Of course,the grooving action of the slitter wheel 60 along the line of cut 80 inadvance of the knife 59 reduces the cutting force required by the flattop cutter.

Thus has been described an underground pipe bursting tool, an apparatus,and a method which achieve all of the objects of the invention.

What is claimed is:
 1. A method for bursting a length of undergroundsteel pipe comprising the steps of slitting through the wall thicknessof said pipe in the longitudinal direction of said pipe along only oneline of cut and progressively spreading said slit pipe wall laterallyalong said one line of cut, said spreading being performed eccentricallywith respect to the longitudinal axis of said pipe length in thedirection therefrom towards said one line of cut using a generallyconical-shaped spreader having an apex end received within said slitpipe and a base end which is larger than the diameter of said pipe,while maintaining a conical-surface surface-generating element of saidspreader in longitudinal adjacent relation to the interior surface ofsaid pipe on the side thereof opposite to said one line of cut.
 2. Amethod according to claim 1, wherein said pipe length extendssubstantially horizontally, and said one line of cut is made alongsubstantially the underside of said underground pipe length.
 3. A methodaccording to claim 1, which further comprises grooving the inner surfaceof said pipe substantially along said one line of cut in advance of saidslitting thereof, said grooving and slitting being performedsubstantially from the interior of said underground pipe.
 4. A methodaccording to claim 3, wherein said length of underground pipe hasexternally attached pipe coupling or clamping means having lengthextending along a portion thereof, and said grooving step is performedat a constant distance in advance of said slitting step which is atleast as great as said length of said pipe coupling or clamping means.5. A method according to claim 3, wherein said grooving step isperformed using a roller type pipe slitting tool.
 6. A method accordingto claim 1, wherein said slitting and expanding steps are performedprogressively along said pipe length, and said spreading stepconcurrently and progressively induces increased hoop tension withinsaid pipe immediately in advance of the location of said slittingtherealong.
 7. A method for bursting a length of underground steel pipeand inserting plastic piping therein, said pipe having external pipecoupling or clamping means attached thereto at at least one undergroundlocation therealong, comprising the steps of pulling a pipe burstingtool from its forward end through said pipe length to slit said pipe andeach of said pipe coupling or clamping means along only one line of cuttherethrough and to laterally spread said slit pipe along its length,said lateral spreading being progressively induced by an eccentricallydisposed conical-shaped spreader portion of said pipe bursting tool, andaugmenting said pulling using repeated hammering on the rearward end ofsaid pipe bursting tool at least during its movement past each of saidpipe coupling or clamping means, said pipe being slit using a fixedknife blade projecting angularly outwardly and rearwardly from saidbursting tool and a rotary pipe grooving tool longitudinally alignedwith said knife blade and projecting outwardly from said bursting toolat a location spaced forwardly away from said knife blade.
 8. A methodaccording to claim 7, wherein said pipe has nominally four-inch (4")diameter, and the force of said pulling is within the rang of fromsubstantially five tons to substantially twenty tons, and said hammeringis at a rate within the range of from substantially 420 to 620 blows perminute using an impact force of from substantially 70 lbs. to 190 lbs.per blow.
 9. A method according to claim 7, wherein said pipe length isdisposed horizontally, and said one line of cut is made along theunderside of said pipe length.
 10. A method according to claim 7,wherein said spreading concurrently and progressively induces increasedlocalized hoop tension within said pipe immediately in advance of thelocation of said slitting therealong, and which further comprisesgrooving the inner surface of said pipe substantially along said oneline of cut before said localized hoop tension is induced therein, saidgrooving, slitting and spreading being performed from substantially theinterior of said underground pipe.
 11. A method for bursting a length ofsteel pipe comprising slitting through the wall thickness of said pipein the longitudinal direction of said pipe along only one line of cut bymoving a fixed slitting blade along said one line of cut while inducinglocalized hoop tension progressively within said pipe on said line ofcut immediately in advance of said slitting blade as it moves therealongusing a generally conical-shaped spreader having an apex end receivedwithin said slit pipe and a base end which is larger than the diameterof said pipe, while maintaining conical-surface a surface-generatingelement of said spreader in longitudinal adjacent relation to theinterior surface of said pipe on the side thereof opposite to said oneline of cut.
 12. A method according to claim 11, which further comprisesgrooving the inner surface of said pipe substantially along said oneline of cut progressively in advance of said progressive inducing oflocalized hoop tension within said pipe.
 13. A method according to claim12, wherein said localized hoop tension is induced by spreading saidslit pipe wall eccentrically with respect to the longitudinal axis ofsaid pipe length in the direction therefrom towards said one line ofcut, said spreading being performed progressively from a fixed distancerearwardly of said slitting blade as the latter moves along said line ofcut.
 14. A method for bursting a length of underground steel pipecomprising the steps of grooving the inner wall surface of said pipelength longitudinally along only one line, and inducing localized hooptension within the pipe wall progressively on and along said groovedline to split and spread the pipe wall laterally apart, said localizedhoop tension being progressively induced by laterally spreading the pipewall eccentrically with respect to the longitudinal axis of said pipelength in the direction therefrom towards said one grooved line using agenerally conical-shaped spreader having an apex end received withinsaid grooved pipe and a base end which is larger than the diameter ofsaid pipe, while maintaining a conical-surface surface-generatingelement of said spreader in longitudinal adjacent relation to theinterior surface element of said pipe on the side thereof opposite tosaid one line.
 15. A method according to claim 1, wherein said spreaderhas the shape of a right circular cone.